Snap-action device



Nov. 7, 1939.

G. A. NVELSON' SNAP-ACTION 'LDEVICE Ffled April. so; 1933 g m /iiiii ATTORNEYS Patented Nov. 7, 1939 UNITED STATES PATENT OFFICE SNAP-ACTI()N DEVICE Gustaf A. Nelson, Brooklyn, N. Y; v Application April 30, 1938, Serial No..205,169

1 Claim. 101. 74-109 The present invention relates to a device for producing a mechanical snap-action in response to applied pressure, particularly where that pressure produces an actuating movement of small magnitude. The snap-action may be utilized for the operation of various useful devices such as indicating means, electrical switching means, valving mechanism for gas or liquid, or other mechanism wherein it is desired to produce a positive, sudden movement) when an applied forcefsuch as fluid pressure, for example, has reached a predetermined point.

One of the principal applications of the invention at present contemplated is in a pressureresponsive electrical switch and the invention is described herein as-it is embodied in the preferred form of such a switch. It-will be apparent, however, from a consideration of the following description, that in place of the moving element of the switch one might substitute valving mechanism or an indicating means for giving a visible or audible signal.

junction with switching, valving or other control mechanisms.

Electrical snap switches of various types are at present in use to a large extent for the automatic control of temperature in many applications, among which may be mentioned electric refrigeration and the lead-pots of type-casting machines. In general, it may be said that these switches are operatedby mechanism which produces movement of an. actuating member in response to temperature changes. 'I'his movement may be the result of fluid expansion acting on a' bellows or diaphragm or of the differential ex-- ture variations of from to 25 R, which is a variation too great for accurate control'of the quality of the type cast.

It is, therefore, an object of the'present invention to provide a device which will operate in accordance with small pressure differentials and with very small magnitudes of movement of the actuating member. A switch has been constructed in accordance with the invention which will operate with as little as 0.002 of an inch- Or such indicating 7 means might be simultaneously operated in con- I Devices movement of the actuating device and will control temperature within a range of 4 F.

Another disadvantage of present switches is that the pressure under which the contacts are held together is decreased so gradually, as the mechanism approaches the point where the contact is broken, that there exists a period just prior to the intendedbreaking of contacts, during which. there issubstantially' no pressure so that if the switch is'subject to vibration, as is frequently the case, the contacts will chatter and arcing will take place. It is therefore a further object of this invention to eliminate this difficulty by holding the contacts together under positive pressure until they are positively opened with a snap.

' of more costly and complex devices.

The present invention also has as objects the provision of suitable means for supporting and regulating the spring member which produces the snap-action in its operative relation toassociated 7 angles to Fig. 1 and on the line 2-2 thereof.

Fig, 3 is a transverse section on the line 3--3 of Fig. 1.

Figs. 4 and 5 are side views of the spring member in relation to its associated parts, illustrating the two positions assumed by the said spring during operation. All of the figures are enlarged relative to the actual device.

. The essential feature of the invention is a spring member, having a single normal or static position which will suddenly jump or snap to a certain point or area of the spring. These positions are herein designated for convenience as the normal and secondary positions respectively.

A preferred embodiment of this spring member is shown in the drawingat l0. As shown in different position when pressure is applied to a s rounded by the spacing sleeves 24.

Fig. 2 this spring comprises a generally rectangular body portion having openings therein which define an internal grid having the configuration of a Y. a A pair oi integral side members H and I 2, extending substantially parallel to the sides of the body portion, provide means for supporting the spring and a tongue 4 provides means for attaching a member to be operated by the spring, such as the strip of insulation l5 secured. thereto by rivets |6. -The spring, together with its integral supports, tongue and grid, may be made by stamping it out of any suitable metal, such as beryllium-copper alloy, phosphor-bronze or the like.

To produce in the spring its capacity for snapaction it is necessary to distort certain portions out of their original plane, slightly increasingtheir length. In a spring shaped as is shown in the drawing this is done by pressing the branch segments l8 and I9 in suitable dies to give them a slight permanent stretch. This distorts the Y-shaped grid composed of the segments l8 and I9 and the central segment 20 with a permanent set outside of the original plane of the spring.

The extent of this distortion is important. It should not be carried so far that pressure applied upon the distorted portion in a direction toward the original plane of the spring will cause it to buckle permanently in the opposite direction with what may be termed an over-center action.. On the contrary, the distortion should be such that when the grid segments are pressed toward the original plane, the spring as a whole will buckle slightly with a snap-action and when the pressure is released it will snap back to its original position, Thus the spring has a single normal position and a secondary or buckled position in which it is under a stress tending to return it to its normal position.

The distortion necessary to produce a snapaction and short of that which will result in the undersired over-center action is very slight and the movement of the distorted'p'ortion which will result in buckling into the secondary position is correspondingly small, usually less than 0.01 of an inch. As hereinafter explained, the extent of that movement can be reduced by proper adjustment of the mounting and adjusting devices for the spring to the order of 0.002 of an inch.

The manner of mounting the spring to utilize its snap-action for electric switching purposes is shown in the drawing. A frame is constructed of upper and lower metal plates 2| and 22 held in spaced relation by thefour corner bolts 23, sur- There are also two center bolts 25 carrying sleeves 26 and 21 between which the perforated, ends of the side members II and I2 of the spring ID are clamped;

and in that way the spring I0 is supported intermediate the plates 2| and 22.

The end of the rigid strip |5 of insulating material carries a metal cross-bar 28 having contacts 29, the bar being secured to the strip l5 by the ears 30 which pass through openings and are bent over upon the strip. A pair of lower terminals 3| and 32 are mounted on an inner sheet of insulation 33 which, together with an outer sheet of insulation 34 and suitable bushings, separates the terminals from the metal plate 22. A pair of similarly insulated upper terminals 35 and 36 are located above and spaced from the lower terminals. The cross-bar 28 reciprocates between these terminals, snapping from one set to the other, thus controlling two circuits if desired.

. pressure of the fluid behind stud 45 presses on segment The bolts 38 and 39 provide means for connecting the switch in a circuit.

The operating mechanism shown in the illustrative embodiment is designed for operation by fluid pressure which would be conducted to the switch through the pipe 40 which is secured to a diaphragm carrier 4| by brazing 4|a. Carrier 4| is threaded into an opening in plate 22 and locked therein by a nut 42. In the carrier is a diaphragm'43 of the usual circular corrugated type which is free to move in response to the of the diaphragm is a fiat-bottomed rider 44 having a centrally placed stud 45 and an upwardly-extending yoke 46. The parts are so mounted relative to one another that the stud '45 presses against the center segment 20 of spring l0 when the diaphragm is moved toward the spring I!) by pressure. The two arms of the yoke 46 are reduced in size at their upper ends 41 and are inserted in holes in the free end of a leaf spring 48 which is secured to plate 2| at its opposite end by a bolt 49.

- pressure results from the heating of the fluid contained in a closed system, the tension of spring 48 likewise determines the temperature at which the switch will be operated. The screw 50 therefore provides means for adjusting the switch for operation at different temperatures as is usual,,

for example, in refrigerators.

In mounting'the spring ID in the mechanism described above,-it is supported primarily on the posts 25. This is a very flexible mounting, how

ever, due to the length and resilience of the side members and I2. It is necessary to further support the spring l0, first, to'press it against one set of contacts together and, second, to support it against the pressure of stud 45 for the production of a snap-action. This further support is obtained from screws 52 which press against and have sliding engagement with the spring I0 at the points shown in Fig. 2. They are adjusted to raise the plane of the normal position of the spring above the level of contacts 35 and 36. This causes the cross-bar28 to press its contacts 29 against contacts 35 and 36 as shown in Fig. 4. In assembling spring ID in the switch it can be initially located by bending the side members and |2 so that in its normal position the conthis position until pressure is applied to the dia-v phragm.

As stated above, grid segments l8 and I9 are distorted out of the plane of spring I0 and when the spring is assembled this distortion extends toward the direction from which the actuating pressure will be applied, i. e., toward stud 45. When the diaphragm moves toward spring I, the

20and moves it toward its original undistorted Between. the ends of spring 48 an adjusting screw 50 is mounted in it. Mounted on top position. This puts a low temperature heater.

segments l9, l9 and 20 under compression and the adjacent sides of spring under tension. When a certain critical point is reached, the

spring l0 buckles or snaps into the position of screws52, its flexing movement is substantially unimpeded.

Attention is called to the fact that the pressure which snaps the spring from the position of Fig. 4' to that of Fig. 5 is applied in a direction tending to move contacts 29 toward contacts 35 and 36, so that there is an increase rather than a decrease of pressure between the contacts until the instant of buckling, when the spring snaps the contacts 29 to the other pair of stationary contacts 3| and 32.

Since pressure on diaphragm 43 may increase beyond the critical snapping point, the rider 44 may go on pushing spring I0 after it has buckled and, unless restrained, may lift it as a unit, separating contacts 29 from 3| and 32. The switch may be adjusted to so operate, if desired, which may sometimes be advantageous. For example, the upper contacts 35, 36 may control a high temperature heater and the lower contacts 3|, 32 As the temperature rises the heat is switched from high to low and if it continues to rise the contacts open and the heat is shut off entirely. As the temperature falls the low heat is turned on and if it falls further the high heat is turned on.

On the other hand it may be desired to operate .-the switch only between the upper and lower contacts without any open position. In such a case the upward movement of rider 44 is'impeded after it reaches the snapping point by a suitable stop such as the screw 54 which may be adjusted to limit the movement of spring 48 and.

of rider 44. g 7

Reference was made above to the fact that spring ID has a single normal position and a secondary or buckled position in which it is under a stress tending to return it automatically to normal position. These two positions would be assumed by the spring'in' the switch shown ex-' cept for the fact that the opposite sets of contacts 3!, 32 and 35, 36 limit its movement. The upper contacts hold the spring somewhat below its normal position and the lower contacts hold it somewhat above its secondary position. It will be realized that by moving the contacts closer together the movement of the spring on either side of its critical snapping point can be reduced. This in turn diminishes the distance through which the distorted segments of the spring must be moved to produce the snap-action and so enables the switch to be operated by extremely small actuating movements. By setting the upper and lower contacts to limit the travel of con tacts 29 to about "1 5' of an inch, for example, the

actuating movement of stud 45 can be reduced to 0.002 of an inch. This fact is an especial advantage because it makes possible the'use of a small diaphragm, which is limited to a small movement, which is inexpensiva compact, rugged and easy to manufacture whereas other devices for similar. purposes require mechanism capable of pro-" ducing much greater movement and are much more costly.

In the switch selected to illustrate the invention the snap-'actionis p uced by holding the spring stationary by screws 52 and pressing segment' toward them with stud 45. It is obvious that the same result should be reached formed from a fiat sheet and having a generally rectangular body portion from one end of which extends a tongue cooperating with means to be actuated, said spring member being provided on eachside of said body portion with side "members extending substantially parallel to the sides 1 of said, body portion and in the same general direction as said tongue, said body portion being distorted out of the original plane of the spring member to such an extent that the latter has a single normal position and a secondary position in which it is under stress tending to return it to normal position means for rigidly supporting the ends of-said side members, and supporting means having a sliding engagement with the body portion of said spring member at the end opposite the end from which the said tongue ex tends, and means for causing relative movement between the distorted body portion of said spring member and the rest of the spring member to cause the latter to buckle and assume its sec- 

